The development of resistance to chemotherapy and immunotherapy is a major obstacle in prolonging survival of cancer patients. The emergence of chemoresistance and immunoresistance were traditionally viewed as parallel and unrelated events, but more recent evidence indicates that overexpression of some immune checkpoint molecules may negatively influence antitumor immunity and also render tumor cells resistant to chemotherapeutic agents (Tamura et al., Leukemia: Official Journal of the Leukemia Society of America, Leukemia Research Fund, UK 27:464-472, 2013; Ghebeh et al., Breast Cancer Res 12:R48, 2010; and Liu et al., Molecular Cancer Ther 10:960-971, 2011).